The present invention relates generally to the correction of focus and distortional errors inherent with conventional head-up display units. More specifically, the present invention relates to a method to correct temperature induced focus and distortion errors in a head-up display unit attributable to plastic lens trains and conventional cathode ray tube electron beam designs.
Ever since the early days of vehicle pioneering, there has always been an inherent danger when an operator of a vehicle, such as a pilot of an aircraft or driver of an automobile, must look down from his outward line of site to view important operative status concerning his vehicle. Such status information is normally presented via analog means such as dials, gauges, or gyroscopes, or digital means such as computer readouts, on a readout display, such as an automobile dashboard or pilot""s information panel. The operative status may include information such as fuel, speed, direction, orientation, weapons status, and the like.
As such, when the vehicle operator temporarily looks to the vehicle information display to gather this important information, his outward line of sight is momentarily disrupted. This has inherent dangers, especially in fast moving vehicles such as aircraft and the like. Furthermore, once a vehicle operator is finished gathering the pertinent information, which may take a fraction of a second or sometimes minutes, he must then return to his original line of sight and his focus must readjust. These continual visual diversions relates to problems such as tunnel vision and focus impairment.
It should be noted, however, that the disclosure herein will concentrate on aircraft head-up display devices and enhancements. However, the present invention is applicable to not only aircraft, but also any type of vehicle which may incorporate the usage of a head-up display. As such, the description and emphasis of the present invention""s usability within an aircraft should not be deemed limiting, but rather an explanation and exemplification of the present invention.
U.S. Pat. No. 3,205,303, to Bradley, issued on Sep. 7, 1965 (""303 patent) attempts to remedy these problems by inventing a remotely controlled remote viewing system. The ""303 patent is one of the first so-called xe2x80x9chead-up displayxe2x80x9d (HUD) units which allows a vehicle operator to receive pertinent vehicle information within his outward line of sight. As such, the vehicle operator does not have to continuously look down to the information display panel to view this information.
There have subsequently been many enhancements and improvements to the ""303 patent. For example, U.S. Pat. No. 3,291,906 to Ward et al., issued on Dec. 13, 1996, discloses aircraft visual indicating or display systems utilizing a cathode ray tube; U.S. Pat. No. 3,666,887, to Freeman, issued on May 30, 1972, discloses a head-up display; U.S. Pat. No. 4,763,990, to Wood, issued on Aug. 16, 1988, discloses a head-up display system; U.S. Pat. No. 5,007,711, to Wood et al., issued on Apr. 16, 1991, discloses a compact arrangement for head-up display components;
U.S. Pat. No. 5,805,119, to Erskine et al., issued on Sep. 8, 1998, discloses a vehicle projected display using a deformable mirror device; and U.S. Pat. No. 5,379,132, to Kuwayama et al., issued on Jan. 3, 1995, discloses a display apparatus for a head-up display system.
The HUD has subsequently become an important component of the instrumentation in high performance aircraft of all types, from tactical fighter aircraft to large commercial transports. By projecting into the pilot""s view an accurate and properly aligned real-time representation of the aircraft""s orientation and environment, the pilot is enabled to control an aircraft more efficiently and effectively through the transition from visual orientation to instrument orientation and back again, while having at all times an accurate representation, either digital, analog or both, of all major flight instruments and weapons systems controls.
However, inherent with the pertinent information that a HUD displays, a clear, accurate, and precise information projection to the pilot is tantamount. As such, temperature induced errors must be kept to an absolute minimum in order to make the HUD effective. Visualization errors and distortion cannot be tolerated in these finely tuned assemblies. However, inherent with a HUD""s use, constant temperature variations and distortions associated therewith are omnipresent and methods and processes of combating these problems are continuous.
The main component of any conventional HUD is its optics. The optics is the assembly which conveys and magnifies the information in a viewable display to the pilot. Some HUD assemblies utilize a lens train (assembly of lenses within an optical alignment) of conventional glass lenses. However, this process has many limitations.
For example, glass lenses are more susceptible to misalignment due to their weight and subsequent focal sag, can be easily damaged or cracked due to extreme temperature and vibrational variables, and are extremely expensive both to produce and maintain.
However, modern computer-designed aspheric plastic lenses have fewer elements than comparable glass lenses and are much lighter and smaller as well, making the lens train much shorter, less complex and more manageable when compared to conventional glass. These aspheric plastic lenses are conventionally made by molding or turning a plastic blank with diamond tooling followed by fine polishing.
Nevertheless, a limitation with all plastic lenses is that they have relatively higher coefficients of thermal expansion compared to glass, and therefore must be corrected for expected projection errors, due to the continuous variations in temperature encountered in an operating aircraft environment. Because of the previously mentioned need for precise and accurate positioning of information in a HUD, it is thus necessary to correct for distortion of the image caused by the cathode ray tube (CRT) electron beam used in conjunction with the lens train.
The present invention overcomes the disadvantages and/or shortcomings of known prior HUD alignment and distortion correction methods and apparatus and provides significant improvements thereover.
The present invention solves the problem of compensating for back focal length changes in the conventional lens systems within a head-up display due to continuous and inherent temperature changes in the aircraft operating environment. The present invention accomplishes this by mechanically measuring and generating an error correction input based upon the differential coefficients of thermal expansion (xcex94xcex1) between the metallic mounting components of the HUD and the HUD""s plastic lens train assembly and subsequently relaying this information to a control means which can alter the CRT position.